An exhaust gas sensor may be positioned in an exhaust system of a vehicle to detect an air-fuel ratio of exhaust gas exhausted from an internal combustion engine of the vehicle. The exhaust gas sensor readings may be used to control operation of the internal combustion engine to propel the vehicle, such as engine air-fuel ratio.
Degradation of an exhaust gas sensor may cause engine control degradation that may result in increased emissions and/or reduced vehicle drivability. Accordingly, accurate determination of exhaust gas sensor degradation and subsequent adjustments to parameters of an engine air-fuel ratio controller may reduce the likelihood of air-fuel ratio errors based on readings from a degraded exhaust gas sensor. In particular, an exhaust gas sensor may exhibit six discrete types of degradation behavior. The degradation behavior types may be grouped into filter type degradation behaviors and delays type degradation behaviors. An exhaust gas sensor exhibiting filter type degradation behavior may have a degraded time constant of the sensor reading while an exhaust gas sensor exhibiting delay type degradation behavior may have a degraded time delay of the sensor reading. In response to sensor degradation, air-fuel ratio controller parameters may be adjusted to increase accuracy of the readings of the degraded exhaust gas sensor.
Additionally, sensors may have other forms of degradation that are diagnosed. For example, exhaust gas sensors, such as oxygen sensors, may become stuck in-range. Such degradation is typically diagnosed by monitoring the sensor over an extended period where air-fuel ratio is expected to change, and identifying degradation if the sensor does not change as expected. However, such identification approaches may take a significantly long time and can be prone to mis-diagnosing the condition.
The inventors herein have recognized the above issues and identified an approach to at least partially address them. In one example, an engine method includes indicating degradation of an air-fuel ratio sensor L-R (lean to reach) and R-L (rich to lean) asymmetry, as well as stuck in-range degradation, based on a central peak of a distribution (such as a generalized extreme value distribution) of sensor reading differentials collected during selected engine operating conditions. In this way, the processed data identifying the central peak information may be re-used to identify and indicate multiple types of sensor degradation. Further, since different default action may be taken depending on the type of degradation, improved default actions may be provided.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.